Denver is in a race against the calendar and the thermometer, trying to figure out which street and park trees can handle hotter summers, deeper droughts, and a growing lineup of pests. Researchers and city foresters are testing new species in real time and speeding up plantings in hopes of keeping neighborhoods livable as the current canopy ages out.
Colorado State University research scientist Jonathan Martin has set up an experimental grove on the CSU Spur campus in north Denver, planted in late 2024. Roughly 80 trial trees are hooked up to irrigation tubes and soil sensors so researchers can track how each one responds when the water gets scarce. Among the contenders is the bigtooth maple cultivar Mesa Glow, developed from trees near Las Cruces, which researchers say could be cold-hardy and drought-tolerant enough to make it in Denver, according to New Mexico State University.
A race against beetles and heat
The high-tech experiments are unfolding while Denver stares down the emerald ash borer and an uneven, aging canopy that leaves some blocks sweltering and others comfortably shaded. The city has hundreds of thousands of ash trees, and community programs are already pushing residents and property owners to treat, remove, and replace them in order to blunt the pest’s advance, according to the Be a Smart Ash program.
Planting sprints and where new trees go
City leaders recently ordered a planting sprint that hit a roughly 4,500-tree goal for 2025, nearly doubling the roughly 2,500 trees Denver’s forestry team usually plants in a year. That burst of activity bought a little time, but foresters warn that the job is not done just because a sapling hits the sidewalk. Those young trees will need larger soil volumes, steady watering, and long-term care if they are ever going to turn into the kind of mature shade the city is counting on, per the Denver Climate Project.
Why variety and speed matter
Researchers say that simply planting faster will not save Denver’s canopy if the tree mix is wrong. Many neighborhoods still lean heavily on a few popular species that are unlikely to thrive in the hotter, drier decades that are coming. The numbers highlight how uneven the canopy already is: Sun Valley had roughly 4 percent tree cover, while Wellshire and South Park Hill were about 35 percent in 2020, and the average street tree in Denver measures under nine inches across. As the Denverite reports, CSU’s Jonathan Martin sums it up by saying, “we need speed.”
Martin and city foresters hope the field trials will convince officials to add tougher new cultivars to the city’s approved right-of-way lists and to steer more planting toward heat-vulnerable blocks. How quickly Denver updates its Urban Forest Strategic Plan and its funding priorities will decide whether this year’s saplings grow into decades of dependable canopy or wind up as just another lost round of planting, according to the City and County of Denver.
